Home in means to direct on a target. The phrasal verb derives from the 19th-century use of homing pigeons, but it resurged in the 20th century to refer to missiles that home in on their targets. It’s also commonly used metaphorically, where to home in on something is to focus on and make progress toward it.
Hone in began as an alteration of home in, and many people regard it as an error. It is a very common, though, especially in the U.S. and Canada—so common that many dictionaries now list it—and there are arguments in its favor. Hone means to sharpen or to perfect, and we can think of homing in as a sharpening of focus or a perfecting of one’s trajectory toward a target. So while it might not make strict logical sense, extending hone this way is not a huge leap.
Outside North America, home in prevails by a huge margin. It also prevails in North America, but only by a ratio of about two to one. Hone in is common even in technical, scientific, and military contexts, where one might expect home in to prevail. A few American and Canadian publishers clearly favor home in as a matter of policy, but most apparently have no strictly enforced policy one way or the other.
Bone cancer is sometimes treated with radioactive isotopes that home in on the bone. [NY Times]
But now the sharks were starting to home in on the large groups that had amassed during the past thirty-six hours. [In Harm's Way, Doug Stanton]
But they do reveal Dahl’s uncanny ability to home in on the darker reaches of human ingenuity. [Financial Times]
Unlike some of his other films, though, which home in on the ways in which sex and violence overlap, La tarea analyses sexuality in a humorous context. [A Companion to Latin American Film, Stephen M. Hart]
Burke advises students to hone in on departments in which they are comfortable and already feel close to professors. [Swarthmore Phoenix]
Other resources like HDTv Antenna Labs provide relatively easy ways to hone in on the right antenna. [Wired]
It’s not the first multinational to hone in on one of the largest vegetarian markets on earth. [Toronto Star]